Dark Matter Quantum Information Science
Dark Matter/Quantum Information Science

Single Microwave Photon Detectors (SMPDs)

Photon counting offers a significantly lower-noise alternative to traditional linear amplifiers for measuring certain signals. At optical frequencies, we have a number of mature technologies for photon counting relying on electrical excitations in semiconductors or gases. Microwave photons are orders of magnitude lower in energy than optical photons, carrying anywhere from 1 ueV to 1 meV of energy (300 MHz to 300 GHz), and therefore require new entirely new detection techniques.

Superconducting qubits provide an appealing platform for developing these detectors. In the circuit QED architecture, superconducting qubits are engineered to couple strongly to electromagnetic modes. While transmon qubits have traditionally operated in the 4-8 GHz frequency range, a subset of the microwave band, there is no fundamental barrier to designing them for a much broader frequency spectrum. The sensitivity of superconducting qubits to quantized transmission line photons was first demonstrated in 2007.

The Quantronics group at Paris-Saclay university has made significant progress recently in utilizing superconducting qubits for itinerant photon detection using a four-wave mixing scheme, developing a single microwave photon detector (SMPD). Our group aims to advance this technology by making a more widely tunable SMPD while also improving detector efficiency and reducing dark counts.

Sensitive measurement of single microwave photons has great applicability to the search for the QCD axion, a dark matter candidate which may have mass from 1 kHz to about 10 THz. The 5-50 GHz range predicted by post-inflationary axion scenarios is particularly attractive and is synergistic with the quantum-sensing advancements that have been made in this frequency range. In combination with a volume-enhanced cavity (see ADMX-VERA), an SMPD could provide unprecedented sensitivity to the theoretically well-motivated DFSZ axion.

Recent Talks by DMQIS Group Members:

packaged SMPD
Packaged SMPD designed and fabricated by the DMQIS group at Stanford
SMPD design
SMPD design made by the DMQIS group. At the center is a conventional transmon qubit, coupled to an input and output (buffer and waste) resonator respectively. A drive line is included to allow for qubit state preparation.
SMPD qubit
Close-up picture of the transmon with coupling capacitors to the respective resonators.